# std::erase, std::erase_if(std::basic_string)

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< cpp‎ | string‎ | basic string

Defined in header `<string>` |  |
| (1) |
template< class CharT, class Traits, class Alloc, class U > constexpr std::basic_string<CharT, Traits, Alloc>::size_type erase( std::basic_string<CharT, Traits, Alloc>& c, const U& value ); |  | (since C++20) (until C++26)
template< class CharT, class Traits, class Alloc, class U = CharT > constexpr std::basic_string<CharT, Traits, Alloc>::size_type erase( std::basic_string<CharT, Traits, Alloc>& c, const U& value ); |  | (since C++26)
template< class CharT, class Traits, class Alloc, class Pred > constexpr std::basic_string<CharT, Traits, Alloc>::size_type erase_if( std::basic_string<CharT, Traits, Alloc>& c, Pred pred ); | (2) | (since C++20)

1) Erases all elements that compare equal to value from the container. Equivalent to

    auto it = std::remove(c.begin(), c.end(), value);
    auto r = c.end() - it;
    c.erase(it, c.end());
    return r;

2) Erases all elements that satisfy the predicate pred from the container. Equivalent to

    auto it = std::remove_if(c.begin(), c.end(), pred);
    auto r = c.end() - it;
    c.erase(it, c.end());
    return r;

### Parameters

c | - | container from which to erase
value | - | value to be removed
pred | - | unary predicate which returns ​true if the element should be erased. The expression pred(v) must be convertible to bool for every argument `v` of type (possibly const) `CharT`, regardless of value category, and must not modify `v`. Thus, a parameter type of CharT&is not allowed, nor is CharT unless for `CharT` a move is equivalent to a copy(since C++11). ​

### Return value

The number of erased elements.

### Complexity

Linear.

### Notes

Feature-test macro | Value | Std | Feature
--- | --- | --- | ---
`__cpp_lib_algorithm_default_value_type` | `202403` | (C++26) | List-initialization for algorithm (1)

### Example

Run this code

    #include <iomanip>
    #include <iostream>
    #include <string>

    int main()
    {
        std::string word{"startling"};
        std::cout << "Initially, word = " << std::quoted(word) << '\n';

        std::erase(word, 'l');
        std::cout << "After erase 'l': " << std::quoted(word) << '\n';

        auto erased = std::erase_if(word, [](char x)
        {
            return x == 'a' or x == 'r' or x == 't';
        });

        std::cout << "After erase all 'a', 'r', and 't': " << std::quoted(word) << '\n';
        std::cout << "Erased symbols count: " << erased << '\n';

    #if __cpp_lib_algorithm_default_value_type
        std::erase(word, {'g'});
        std::cout << "After erase {'g'}: " << std::quoted(word) << '\n';
    #endif
    }

Possible output:

    Initially, word = "startling"
    After erase 'l', word = "starting"
    After erase all 'a', 'r', and 't': "sing"
    Erased symbols count: 4
    After erase {'g'}: "sin"

### See also

removeremove_if | removes elements satisfying specific criteria (function template)
ranges::removeranges::remove_if (C++20)(C++20) | removes elements satisfying specific criteria (algorithm function object)

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